The disposal of dairy effluent in Hawaii is a current concern because of possible contamination of surface, subsurface and coastal water as well as increased costs resulting in the closure of many dairies. This study was conducted to assess the removal of inorganic N, phosphate, organic matter (COD) and fecal coliform in dairy effluent and reduce the costs of doing so using MSL (Multi-Soil-Layer) systems. Four MSL systems were constructed with two replications of two treatments. Treatments were Perlite or the Leilehua soil in the aerobic layer, and a mixture of charcoal, sawdust, iron filings and Honouliuli soil in the anaerobic layer. Dairy effluent was applied to each system and the MSL-treated effluent was collected every week and analyzed for inorganic N, phosphate, organic matter (COD) and fecal coliform. The first phase of the study revealed that the removal of inorganic N was similar for the Leilehua and Perlite MSL system which was 22-93% and 21-96% respectively. The phosphate removal was higher in the Leilehua MSL system (64-99%) compared to the Perlite MSL system (9-97%). The removal of organic matter (COD) in Perlite MSL system (4-37%) was greater than in the Leilehua MSL system (3-30%). The removal of fecal coliform was similar for the Leilehua and Perlite MSL system which was 6-99% and 29-98% respectively. The percentage removal of inorganic N by both the MSL systems and phosphate by the Perlite MSL system decreased over time in the first phase. Three possible improvements were made in the second phase of the study to increase the removal efficiency of the MSL systems. Additional aeration increased the removal of phosphate by the Leilehua MSL system. Sucrose application with a constant rate of aeration increased the removal of inorganic N, organic matter (COD), and fecal coliform in the Leilehua and Perlite MSL systems. The removal of phosphate by the Perlite system increased with sucrose additions. The different rates of aeration with constant rate of sucrose enhanced the removal of organic matter (COD) and fecal coliform. This study demonstrated that MSL systems have the potential to remove inorganic N, phosphate, organic matter and fecal coliform in dairy effluent. Some adaptations, such as application of sucrose with constant aeration increased the removal efficiency of the MSL systems. The systems can be very economical due to the nominal cost of the materials used in it.

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